FIG. 18 schematically shows a sectional view of a conventional general rotary electric machine (called a “permanent magnet type synchronous motor” or a “permanent magnet type motor”) as sectioned in a direction perpendicular to a rotation axis thereof.
As shown in FIG. 18, the rotary electric machine has a stator 70 and a rotor 80, and the rotor 80 is arranged inside the stator 70.
The stator 70 has a stator iron core 71 and stator windings 76. The stator iron core 71 is formed of, for example, a plurality of electromagnetic steel plates being laminated in a rotation axis direction, or an iron dust core. The stator iron core 71 has a plurality of tooth sections 72 each having a front end portion which faces the rotor 80. The winding 76 is wound on the tooth section 72, and the tooth section 72 serves as a magnetic pole.
The rotor 80 has a rotor iron core 81 and a plurality of permanent magnets 82. The permanent magnets 82 of FIG. 18 are embedded in the interior of the rotor iron core 81. Alternatively, there is also known a configuration in which a segment-shaped permanent magnet or a ring-shaped permanent magnet is attached to a rotor iron core. The rotary electric machine generates a rotation torque around a rotation axis 90 by means of interaction between a rotation magnetic field generated by the stator 70 and magnetomotive force generated by the permanent magnets 82 of the rotor 80.
The rotary electric machine using the permanent magnet is advantageous in that a high torque is generated even if the rotary electric machine has a small size, but on the other hand involves a problem that a pulsating torque occurs due to interaction between magnetic fluxes of the permanent magnets 82 and the tooth sections 72 of the stator 70. Particularly, a pulsating torque under an unloaded state is called a cogging torque, and may cause deterioration in a positioning accuracy, a vibration, a noise, and the like. In an interior magnet type rotary electric machine having a permanent magnet embedded in the inside of a rotor, there is a problem that the cogging torque is particularly high.
Accordingly, in order to reduce the cogging torque, a technique of using a rotor having a skew structure, providing auxiliary slots in the tooth sections of the stator, or the like, has been developed. The applicant of the present application discloses in Patent Document 1 that a cogging torque can be reduced by providing auxiliary slots extending in a rotation axis direction in tooth sections of a stator and changing the width of the auxiliary slots in the rotation axis direction. Disclosed in Patent Document 1 is a configuration having a combination of a stator with the auxiliary slots and a rotor with a skew structure.
Additionally, a technique of using a rotor having a pseudo skew structure is disclosed in Patent Document 2, for example.
Patent Document 1: Japanese Laid-Open Patent Publication No. 2006-230116
Patent Document 2: Japanese Laid-Open Patent Publication No. 2001-231196